Psychrometers

The psychrometer is one of the instruments used to determine the relative humidity in a room. This consists of two thermometers, one with a dry bulb that measures the air temperature and the other with a wet bulb, i.e. with the bulb covered by a water soaked gauze, which therefore measures a lower temperature due to the heat absorbed by the evaporation of the water. Since this temperature difference is dependent on the humidity of the air, the humidity value can be determined by comparing the two temperatures.

Air can flow over the wet bulb by its natural flow or be forced by a small fan in the instrument: a distinction is made between naturally ventilated and forced-ventilated psychrometers. There are specific standards that regulate the type of instrument to be used depending on the purpose of the measurement.